1. Field of Invention
The present invention relates to a power supply, a controller of the power supply, and a method for controlling the power supply, in particular, relates to those are controlled by a single feedback signal.
2. Related Art
The level of the power factor is a principal standard to evaluate the performance of a power supply, and the level is also required by several relative specifications. There are two methods of the traditional power supply to promote the power factor in general, and the first one is to add a valley-fill circuit as the passive power factor corrector (PFC) circuit after rectifying the AC power. The aforesaid method is easy and inexpensive, however, the passive circuit of this method is unable to trace and regulate the phases of the current and the voltage, so the improvement of the power factor is finite.
The second method utilizes a combination of two various functional circuits to promote the power factor. In the first place, an active PFC circuit is arranged after rectifying the AC power. Then a power circuit for DC to DC conversion is configured after the PFC circuit. The PFC circuit promotes the power factor, and the power circuit provides the function to amplify the power.
The front stage circuit, active PFC circuit, and the rear stage circuit, power circuit for DC to DC conversion, are controlled separately by the independent integrated circuits (IC) or by the independent control circuits in the traditional circuit design. Take boost PFC circuit for example, an IC fetches the wave form that is received by the PFC circuit after rectifying the AC voltage, and the IC takes the output voltage of the PFC circuit as the feedback signal. Then the IC obtains a reference voltage in proportion to an input voltage of the PFC circuit via process including comparison, compensation, and calculation done by the IC. Thereafter, the IC compares the reference voltage with a current of a switch of the PFC circuit to determine whether the IC can turn off the switch or not. The IC also detects the zero current of the PFC circuit to turn on the switch of the PFC circuit. To turn on and off the switch of the PFC circuit, an inphase input current that follows the input voltage variation is obtained to promote the power factor.
Moreover, a flyback converter circuit is a common choice as the power circuit of the rear stage circuit because the flyback converter circuit can both boost and buck the voltage to convert the voltage. In addition, the flyback converter circuit comprises a transformer to isolate the input and the output, further the transformer converts the polarization.
Nevertheless, the flyback converter circuit is controlled by an IC, so the IC produces a control signal to control the switch of the flyback converter circuit. The control signal is produced according to the feedback signal resulted from the output voltage and the other process such as comparison. For the sake of better performance of the power factor and the power, various control circuits and controllers are required in general to control the PFC circuit and the power circuit individually.
Consequently, the whole design of the circuit is more complicated, accordingly, requisite elements, material or size of the circuit increase and enlarge.